Hey guys,
I'm trying to track a problem that's been with me for a while now. The car is a '97 Z28, 3.73's in the rear, BMR panhard rod, and that's about all the mods I have to the rear. When I'm coming to a stop, or just slow-speed driving, the rear of the car sort of grinds. (Could possibly be described as an abrasive humming sound.) For instance, I live in a subdivision...so naturally, I drive slower through here (about 10-15 MPH)...at those speeds and before the car actually stops, there's this grinding noise. The grinding sort of skips a little too. Like: Nannnn nnnnn nn nnnnnnnnnnnnnnnnnnnnn. I can't figure it out. The noise goes away when I give the car more gas also. It doesn't matter whether I'm pushing the brakes or not...makes no difference. It only happens on deceleration. At all other speeds, the rear is quiet...except for the occasional whine from the gears.

The rear end oil is only a few months old. It's an 80/90 lubricant with the GM additive. I've checked everything twice. Control arms are fine...tightened properly. Stabilzer bar, links and bushings are fine. Torque arm is okay. Panhard rod is greased.

The only thing out of place, is on the passenger side, my rotor has a pretty good groove on the outer side of the rotor. The inner side is perfect, as is the driver's side rotor.. I pulled off the caliper this evening on that side, just to check the pads, and it seems to be just regular wear and tear. The pads have plenty of life left. Could this be making that sound? Seems unlikely to me...because like I said before...it doesn't make a difference whether I'm pushing the brakes or not...it grinds regardless. The grinding only goes away when I accelerate.

I don't know what else to do...except to tear into the posi unit, and see what's up. Any advice...or anyone else have a problem like this??

 

I have the same thing and it has also been around for awhile. I definetly agree with 'abrasive humming' but not grinding (no piercing sounds). Your nnnnnn's really remind me of it. Mine happens on deceleration and seems to go away when I get on the gas. Im probably an idiot for not doing anything about it forever, but I was hoping it was my rotors and I was going to replace them soon. Under the car Ive got a leak where the driveshaft meets the diff, but it sounds like your posi looks a-ok externally. Sorry I cant actually help, but atleast I can say you arent the only one.